I was trying to think of an example. My wife didn't know I was answering an italki question. I live near Boston. The local football team is the New England Patriots. I remembered that they had an important game yesterday but didn't know who won. I thought I would use that in my answer, but didn't know who won.
I asked my wife "how did the Patriots do yesterday?" My wife's answer--remember, she didn't know I was answering an italki question!--was:
"Oh, they lost, so everyone is going to be crying in their beer today."
She actually used the idiom!
Suppose person A says "person B is crying in their beer about X." It means B is feeling sorry for himself. Person B is being self-pitying. Person A thinks that X is not very important. Person A thinks person B is being much too self-pitying. It's joking. It's teasing. It's mildly disrespectful.
"I can't believe it. I just can't believe it. How could it happen? It was so close, so close!"
"Oh, quit crying in your beer about it. The Broncos won. Tom Brady isn't Superman. Get over it."